1. Field of Invention
The present invention relates generally to force exerting apparatus and more particularly to a new and improved spreader tool of the type wherein force arms are urged apart by the influence of an axially driven piston which tool may be designed to apply a force to a load which is directly proportional to the axial force of the piston throughout its spreading cycle, or to cause a rate of spreading movement of the force arms which is directly proportional to the rate of axial movement of the piston of the jack, or to produce predetermined variations in the applied force to the load and in the rate of spreading movement of the force arms over the course of the spreading cycle of the tool depending upon the geometrical configuration chosen for the edges of the force arms which engage the piston as hereinafter more fully appears.
2. Brief Description of the Prior Art
It has long been recognized that force exerting devices of the spreader type are useful in connection with the repair of deformed automobile bodies and other structures, and as rescue tools in a wide variety of emergency and accident situations. The principal advantage of such tools resides in the facts that such tools may be lightweight and weildy yet powerful devices capable of use in tight places such as by insertion into narrow crevices in the body of a construction to apply against the sides of same a force derived from the force of a powerful force generating mechanism such as a hydraulic jack. To accomplish this spreader tools have heretofore relied upon numerous variations of a simple linkage method of driving annularly movable force arms with an axially moving piston.
Basically devices of this type consist a fluid operated cylinder, a base member mounted on the forward end of the cylinder, a piston mounted for axial movement in the cylinder extending through the forward end thereof, a pair of force arms pivotally mounted on the base on opposite sides of the cylinder, and a pair of lever arms pivotally connected to the forward end of the piston at one end thereof and pivotally connected to one or the other of the force arms respectively at the other ends thereof such that axial movement of the piston controls the separation of the nonsecured ends of the force arms. Examples of this type of construction are shown in U.S. Pat. No. 265,549 to Urie; U.S. Pat. No. 2,341,278 to Long; U.S. Pat. No. 2,447,401 to Ferguson; U.S. Pat. No. 2,643,562 to Geddes; U.S. Pat. No. 2,497,836 to Miller; and U.S. Pat. No. 3,819,153 to Hurst.
It will be understood that the geometry of devices of the type just described is such that the spreading force, that is that portion of the force applied by the piston which is conveyed to the force arms by the lever arms so as to act at 90.degree. to the axial direction of piston movement, increases as the nonsecured ends of the force arms move away from each other while the rate at which this separation occurs decreases. These geometrical limitations severely effect the efficiency of tools of this type.
Consider, for example, an attempt to open a crash jammed door, to separate crash entangled vehicles, to right an overturned automobile, or even to reshape a deformed fender. In each of these cases the force necessary during the job seldom exceeds the force necessary to initiate movement of the load; yet present spreader devices apply their minimum force initially, increasing force and decreasing spreading rate throughout the spreading cycle. Accordingly, the axial force applied by the piston of such devices must be initially high in order to produce a spreading force adequate to move the load, yet in the typical case, wherein the axial force applied by the piston is constant throughout the spreading cycle, this means that as the spreading cycle continues the spreading force inefficiently exceeds that force necessary to move the load by greater and greater amounts. This may, of course, be avoided by the provision of a drive mechanism for the piston which is variable in relation to the variation in spreading force over the spreading cycle, but such a mechanism is undesirable in this context due to the complexity and weight it adds to such a device. Additionally, the hydraulic pressures which must be generated and maintained to supply the axial forces such devices require are also high requiring expensive and cumbersome equipment for their generation; constant care in the design and maintenance of connecting lines and joints; and careful design of the tool itself in order to avoid stress failures.